An image forming apparatus is an apparatus, for example, a printer, a copying machine, a fax machine and a multi-functional machine having combination of one or more functions thereof, which prints an image on a printing medium such as paper.
An electro-photographic image forming apparatus, which is one type of the image forming apparatus, includes an exposing unit, a transfer unit, a developing unit, a fixing unit and the like, which are disposed in a main body forming the external appearance of the apparatus, to print an image on the printing medium.
Broadly speaking, a printing medium carrying developer image on its surface is subjected to a high-temperature and high-pressure state in the fixing unit to have the developer image fixed on the printing medium.
The fixing unit typically includes rollers rotating in engagement with each other. For example, a heat roller is rotated by a rotational force applied to a press roller. Meanwhile, the heat roller has a belt which is wound on an outer surface of a frame and is rotated.
However, in a conventional image forming apparatus, the lateral slippage of the belt during its rotation may result in, for example, the damages to the belt.